1. Field of the Invention
The present invention relates to an electrode, a secondary battery and a method of producing the same. More particularly it relates to an electrode, a secondary battery and a method of using a valve action metal for a collector to produce the same with an excellent cyclic property and a film forming property.
2. Description of the Related Art
The size and weight of a mobile device reduced progressively in the field of information communication. In response to this recent situation, thin, low-height and high-energy-density batteries and electric double-layered condensers have been developed increasingly.
An electrode structure for configuring the battery or electric double-layered condenser can be produced by applying onto a collector an electrode composite consisting of an active substance powder (activated carbon powder in the electric double-layered condenser), a conductive auxiliary and an organic binder. When the electrode composite is formed on the collector, the collector and the electrode are required to tightly contact with each other in order to allow the electrode to function sufficiently. In particular, if a collector made of a valve action metal (such as Ta, Nb, Al, W, Mo, Ti, and Sr) and an aqueous electrolytic solution are employed in a battery, a DC current flows into the collector and causes a formation reaction in the surface of the valve action metal to produce an oxide film. As a result, there was a disadvantage that the adherent property of the electrode to the collector worsened to lower the cyclic property of a secondary battery. There was another disadvantage that a mixed electrode paste with an aqueous electrolytic solution had a poor film-forming property on the collector because the valve action metal was not excellent in wetting with the aqueous electrolytic solution.
Several methods for improving the adherent property of the electrode to the collector have been proposed in the art. JP 5-182670A discloses a method for roughening the surface of a collector to adhere an electrode to the collector. This method, however, simply increases the physical adherence of the electrode to the collector using an active substance and therefore gradually causes a peel due to repeated expanding and retracting of the active substance. According to another method which is also used commonly, an anchor layer having a composition near that of the film is provided between a substrate and a film. The anchor layer is required, however, to be conductive in order to transfer electrons between a collector and an electrode and thus suffers many restrictions. In addition, a peel occurs when a thick film cracks.
As described above, according to these conventional methods, it is difficult to obtain an electrode for a secondary battery with a high cyclic property. This problem is considered to inhibit an ideal secondary battery from developing.
Accordingly, it is an object of the present invention to provide a secondary battery comprising:
a first collector made of a first valve action metal;
a second collector made of a second valve action metal;
a first electrode;
a second electrode;
a separator; and
an outer can,
wherein said first collector is covered with a first oxide film of a thickness of 1.7-10 nm, said first oxide film being formed in a range of from 30% by area or more to less than 100% by area relative to the surface area of said first collector, said first collector having said first electrode disposed thereon;
said second collector is covered with a second oxide film of a thickness of 1.7-10 nm, said second oxide film being formed in a range of from 30% by area or more to less than 100% by area relative to the surface area of said second collector, said second collector having said second electrode disposed thereon.
It is another object of the present invention to provide an electrode for a secondary battery which comprises a collector made of a valve action metal and a paste film formed on said collector,
wherein said collector is covered with an oxide film of a thickness of 1.7-10 nm, said oxide film being formed in a range of from 30% by area or more to less than 100% by area relative to the surface area of said collector.
It is another object of the present invention to provide a method of producing a secondary battery comprising a first collector made of a first valve action metal, a second collector made of a second valve action metal, a first electrode, a second electrode, a separator and an outer can, wherein said method comprises:
forming a first oxide film of a thickness of 1.7-10 nm on said first collector, said first oxide film being formed in a range of from 30% by area or more to less than 100% by area relative to the surface area of said first collector;
forming a second oxide film of a thickness of 1.7-10 nm on said second collector, said second oxide film being formed in a range of from 30% by area or more to less than 100% by area relative to the surface area of said second collector;
forming said first electrode on said first collector; and
forming said second electrode on said second collector.
It is another object of the present invention to provide a method of producing an electrode for a secondary battery which comprises:
forming an oxide film of a thickness of 1.7-10 nm on a collector made of a valve action metal, said oxide film being formed in a range of from 30% by area or more to less than 100% by area relative to the surface area of said collector; and
forming a paste film on said collector.
Other features and advantages of the invention will be apparent from the following description of the preferred embodiments thereof.